The present invention relates to a blow molding method of forming a hollow product made of resin through a parison, and particularly relates to a blow molding method of removing a flash from the product in a molding operation thereof.
In a conventional blow molding method for forming a hollow product made of resin through a tube-shaped parison, the hollow product is usually formed as follows. At first, the tube-shaped parison made of melted resin is extruded from a die head towards a position between a pair of split molding portions. After tightly closing the molding portions, a high-pressure air is blown into a hollow portion of the parison so as to inflate the parison. Then the parison is reformed in a specified form based on a cavity defined by the tightenly closed molding portions. The thus reformed parison is cooled and solidified within the cavity, to thereby form a molded resin product. In addition to this, a flash which is generated by the remaining parison around the molded resin product must be removed in order to obtain a complete product.
However, the removing operation of the flash is implemented by hand generally. Since the operation is very complicated, it increases manufactured cost thereof. Further, such successively and repetitiously flash removing operation cause to raise a risk of worker""s accident.
It is an object of the present invention to provide a blow molding method which can eliminate a flash removing operation.
The above-mentioned object can be achieved by a blow molding method for forming a hollow resin product, according to the present invention, comprising the steps of:
extruding a parison from a die head towards a position interposed between first and second molding portions, wherein the first molding portion has a first mating surface and a first annular-shaped parison-cutting-protrusion erected from the first mating surface, and the second molding portion has a second mating surface and a second annular-shaped parison-cutting-protrusion erected from the second mating surface;
abutting the first and second annular-shaped parison-cutting-protrusions while closing the first and second molding portions tightly, thereby defining a molding chamber by the first and second annular-shaped parison-cutting-protrusions; and
abutting a plurality of first confronting rods with a plurality of second confronting rods respectively at the same time of the abutting step of the first and second annular-shaped parison-cutting-protrusions, wherein the first confronting rods are protruded from the first mating surface of the first molding portion and disposed outside the first annular-shaped parison-cutting-protrusion in a radial direction of the first molding portion, and the second confronting rods are protruded from the second mating surface of the second molding portion and disposed outside the second annular-shaped parison-cutting-protrusion in a radial direction of the second molding portion.
In the above-mentioned blow molding method, it is preferable that the method further comprises the step of adjusting a length of at least one of first and second confronting rods, the length protruding from the respective mating surface.
In the blow molding method according to the present invention, when the molding portions are tightly closed, not only the first and second parison-cutting-protrusions but also the first and second confronting rods are respectively and simultaneously brought in contact with one another. The protrusions of the mating face are abutting at the same time of abutting a plurality of confronting rods proposed in the periphery of the mating surface of the molding portion. That is, the first and second annular-shaped parison-cutting-protrusions are positioned in such a manner that they are brought in contact with each other at the same time of abutting the confronting rods. Therefore, even if the first and second annular-shaped parison-cutting-protrusions are so edged as to cut the parison, no impact strength in the molding portion closing operation concentrates on such edged protrusions, because dispersion of impact strength toward the confronting rod on the molding portions prevents the edged protrusions from breaking out.
In the blow molding method according to the present invention, it is preferable that each of the first and second confronting rods has a curved surface at its tip end.
With this feature, even if the first and second confronting rods pinch the high-temperature molten parison with pressure, the parison is very easily floating away along the curved surface. Therefore, the first and second confronting rods completely can be brought into contact with each other, even if the confronting rods pinch the high-temperature molten parison.
In the blow molding method according to the present invention, the tip ends of the first and second annular-shaped parison-cutting-protrusions are brought in contact with each other completely and entirely in its circumferential direction without any clearance, so that the prison can be completely decoupled with a flash which are formed outside in the periphery of the protrusions.